The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An airplane is moved by several turbojet engines each housed in a nacelle also housing a set of related actuating devices connected to its operation and performing various functions when the turbojet engine is running or stopped. These related actuating devices in particular include a mechanical thrust reversal system.
As illustrated in FIG. 1, a nacelle generally has a tubular structure comprising an air intake 2 upstream of the turbojet engine, a middle structure 3 designed to surround a fan of the turbojet engine, a downstream section 4 housing thrust reverser means (also called thrust reverser) and designed to surround the combustion chamber of the turbojet engine, and generally ends with a jet nozzle 5 whereof the outlet is situated downstream of the turbojet engine.
Modern nacelles are designed to house a dual flow turbojet engine capable of generating, via the rotating fan blades, a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) that circulates outside the turbojet engine through an annular channel 6, also called a duct, formed between a fairing 7 of the turbojet engine and an inner wall 8 of the nacelle. The two flows of air are ejected from the turbojet engine through the rear of the nacelle. The two flows of air are ejected from the turbojet engine through the rear of the nacelle.
The role of a thrust reverse device is, during landing of an airplane, to improve the braking capacity thereof by reorienting at least part of the thrust generated by the turbojet engine forward. In that phase, the reverser obstructs the cold air flow, and orients that flow toward the front of the nacelle, thereby generating a counter-thrust that is added to the braking of the wheels of the airplane.
The means implemented to perform this reorientation of the cold flow vary depending on the type of reverser. However, in all cases, the structure of a reverser comprises moving parts that can be moved between a deployed (or “reverse jet”) position, in which they open a passage in the nacelle designed for the diverted flow on the one hand, and a retracted (or “direct jet”) position, in which they close that passage on the other hand.
FIGS. 2 and 3 illustrate a traditional cascade vane thrust reverser 40, also known as a cascade reverser, in which the reorientation of the air flow is done by cascade vanes 41, the cowl 42 being slidingly mounted along the axis A of the nacelle so as to expose or cover said vanes 41. Complementary blocking doors 43, also called reverser flaps, activated by the sliding of the cowling, generally allow closing of the annular cold air flow (secondary flow) channel 6 downstream of the vanes 41 so as to optimize the reorientation of that air flow.
This type of cascade thrust reverser 40 is arranged downstream of the fan case 30 of a dual flow turbojet engine, and its associated fan cowl 31. This reverser 40 has at least one moving cowl 42 having an outer panel 420 and an inner panel 421 (or inner diaphragm) designed to delimit, in a direct jet position of the turbojet engine (FIG. 2), an outer wall of the annular channel 6 in which the secondary flow flows, the reverser 40 having at least one reverser flap 43 hingedly mounted on the inner wall 421 of the moving cowl 42 and actuated by at least one connecting rod 45 during the movement of the moving cowl 42 in the downstream direction, such that, in a thrust reversal or reverse jet position (FIG. 3), each blocking door 43 has an area extending in the annular channel 6 so as to deflect at least part of the secondary flow outside said annular channel 6.
This thrust reverser 40 has a plurality of cascade vanes 41, fastened between the front peripheral frame 46 and a stationary rear peripheral frame 47 that generally join the outer panel 420 and the inner panel 421 of the moving cowl 42 between them. During operation, the reorientation of the secondary flow, in the reverse jet position, is done by said cascade vanes 41, the moving cowl 42 primarily having a sliding function aiming to expose or cover said cascade vanes 41, the translation of the moving cowl 42 being done along a longitudinal axis substantially parallel to the axis A of the nacelle 1. A housing 48 is provided in the moving cowl 42 and makes it possible to house the cascade vanes 41 when the thrust reverser 40 is not actuated, i.e. in the direct jet position, as shown in FIG. 2.
The sliding of the moving cowl 42 between its direct jet and reverse jet positions is ensured by cylinders (not shown) distributed on the periphery of the nacelle. Traditionally, these cylinders are fastened upstream on a stationary part of the nacelle, such as the upstream front support frame 46 of the cascade vanes 41, and downstream inside the moving cowl 42, by means of adapted fittings.
More specifically, the actuating rods of said cylinders pass through the downstream rear support frame 47 of the cascade vanes 41 to cooperate with the moving cowl 42. This necessarily means that the upstream rear support frame 47 of the cascade vanes 41 has a certain radial bulk. Furthermore, the vanes 41, in reverse mode or reverse jet position, undergo major aerodynamic loads that tend to cause the downstream portions of the vanes 41 fastened on the peripheral groove frame 47 to emerge outward. The height (or thickness) of the rear frame 47 is advantageously larger than that of the vanes 41 so as to provide the best possible inertia for the vane assembly 41.
In standard thrust reverser structures 40, the thickness of the aerodynamic lines is sufficient to have an adapted inertia of the vane assembly 41 and to be able to pass through the rear frame 47 using the cylinder rod to reach the fastener of the moving cowl 42 downstream of the rear frame 47. To return to the current inertia, the structure of the rear frame 47 is festooned at the opening, increasing the height of the rear frame proportionately.
However, in modern nacelles, where efforts are made to reduce aerodynamic losses due to wet surfaces, the lines are increasingly close together, and it is in particular therefore important to be able to reduce the radial thickness of the rear frame, or even to be able to completely eliminate the rear frame. In fact, it is often more possible to house the rear frame having openings in the moving cowl, the total thickness of the cowl no longer being sufficient to house the entire architecture of the thrust reverser in the nacelle.
To respond to this problem of eliminating the rear frame in cascade thrust reversers, it is known, in particular from patent applications EP 1 852 595 A2 and EP 1 515 035 A2, to use a self-mounted cascade assembly, also called self-mounted cascades, i.e. an assembly of cascades only fastened to each other and to the front frame, with no rear frame.
FIGS. 4 to 6 illustrate one known example of a self-mounted cascade assembly 51. As illustrated in FIG. 4, the thrust reversers 50 with self-mounted cascades 51 have an assembly of several self-mounted cascades 51 that makes it possible to achieve a flexible arrangement of the driving of the reverser layers. The self-mounted cascades 51 are distributed on the periphery of the downstream portion of a peripheral front frame 56 and may form an assembly that may contain up to twelve cascades per half-side of the reverser 50, such as for example for self-mounted cascades 51 per half-side in the example of FIG. 4.
The multiplicity of the self-mounted cascades 51 allows very flexible driving of the reverser layers and makes it possible to use a specific blading configuration in several positions, this ultimately making it possible to control the overall cost of producing the reverser function using cascade vanes.
As shown in FIG. 5, which illustrates a detail of FIG. 4, each self-mounted cascade 51 is provided with a plurality of cells and has two opposite openwork front surfaces, in this case an upper front surface 510 situated toward the outside across from the outer panel 420 of the moving cowl 42, and a lower front surface 511 situated toward the inside across from the inner wall 421 of the moving cowl 42.
As shown in FIG. 6, which illustrates an assembly of two self-mounted cascades 51, each self-mounted cascade 51 has an upstream portion 512 (sometimes called front portion) fastened on the front frame 56 and an opposite downstream portion 513 (sometimes called rear portion) that is free, i.e. that is not fastened to a rear frame. Furthermore, each self-mounted cascade 51 has two opposite side edges extending over the entire width of the self-mounted cascade 51, i.e. an upstream side edge 514 situated in the upstream portion 512 and a downstream side edge 515 situated in the downstream portion 513; the side edges 514, 515 of the self-mounted cascades 51 form the circumferential, or peripheral, edges of the cascade assembly 51 situated in the thrust reverser 50, extending in a bowed manner around the axis A of the nacelle.
Each self-mounted cascade 51 also has two opposite transverse edges 516 extending over the entire length of the self-mounted cascade 51; the transverse edges 516 of the self-mounted cascades 51 form junction edges between the self-mounted cascades 51 of the cascade assembly situated in the thrust reverser 50, said transverse edges 516 extending substantially parallel to the axis A of the nacelle.
To be assembled to one another, each self-mounted cascade 51 has two strips of material 517, substantially parallel to the front surfaces 510, 511, positioned on the two transverse edges 516 and extending over substantially the entire length of the self-mounted cascade 51. In this way, the adjacent strips of material 517 of two adjacent self-mounted cascades 51 overlap one another and are fastened to one another by fastening screws 518. In this way, in this assembly, the self-mounted cascades 51 are fastened to one another over substantially the entire length thereof.
The main drawback of this type of assembly is that it has solid strips of material 517 at successive intervals, between the cascades 51 over substantially the entire length of the cascades 51, thereby limiting the deflection function of the cold air flow by limiting the surface area of the openwork surfaces.
Since the cross-section of the self-mounted cascades 51 should be substantially equal to the section of the annular channel 6, in other words the cold air duct, it is important for the loss of cross-section due to this connection of the self-mounted cascades 51 to one another to be offset by an increased length of said self-mounted cascades 51.
However, the Applicant has noted in practice that excessively long self-mounted cascades 51 do not efficiently deflect the cold air flow in their downstream portions 513. In fact, the longer the self-mounted cascade 51, the less air effectively passes through all of the cells (or blades) of the cascade, with the result that the efficiency of the deflection (and therefore breaking) is reduced during thrust reversal.
Thus, the management of the layers of the reversal flow is more delicate to manage with an assembly of several self-mounted cascades 51; the flexibility obtained by using several individual cascades assembled to one another is lost with this increased length, and each self-mounted cascade 51 cannot be reused on another peripheral sector of the thrust reverser 50. Ultimately, the cost of this assembly of self-mounted cascades 51 then becomes higher than that of using individual cascades.